1. Field of the Invention
Much work has been done on improving the injectivity of water injection wells, i.e., the ability to inject water into an oil-containing subterranean formation through a wellbore, by the removal of residual oil from the formation pore spaces in the near wellbore area. An increase in injectivity, while not resulting in any increase in the amount of oil recovered, does serve to accelerate the rate of recovery of oil, thereby improving the economics of the waterflood process.
There is a substantial and unfulfilled need for improved techniques to increase the injectivity of water injection wells to be used in certain waterflood processes where there is a low formation permeability to water, as compared to the formation absolute permeabilty, due to the presence of residual oil in the formation pore spaces adjacent the injection wells.
2. Prior Art
U.S. Pat. No. 4,690,217 discloses improving the injectivity of a water injection well by removing residual oil from the formation in the near injection wellbore area through injection of an aqueous fluid containing a surfactant having the formula: EQU RO(C.sub.3 H.sub.6 O).sub.a (C.sub.2 H.sub.4 O).sub.b YX
wherein:
R is an alkyl group containing from about 3 to about 20 carbon atoms or an alkylphenol where the alkyl portion of the alkylphenol contains from about 3 to about 20 carbon atoms or a mixture thereof, PA1 a has an average value between 0 and 10, PA1 b has an average value between about 1 and about 10, PA1 Y is a sulfate or sulfonate group; and PA1 X is a cation, preferably monovalent. PA1 R is a linear or branched alkyl radical, an alkenyl radical or an alkyl or alkenyl substituted benzene radical, the non-aromatic portion of the radical containing from 6 to 24 carbon atoms; PA1 m has an average value of from about 1 to about 10, PA1 n has an average value of from about 1 to about 10, PA1 Y is a hydrophilic group such as a sulfate or sulfonate; and PA1 X is a cation, preferably monovalent. PA1 n is an integer from 10 to 40, PA1 m is an integer from 20 to 50, and PA1 Y is hydroxyl, OSO.sub.3 M or SO.sub.3 M, where M is an alkali metal cation or ammonium. PA1 R is selected from the group consisting of an alkyl of 1 to 6 carbon atoms, phenyl and tolyl, PA1 R' is a 1,2- or 2,3-butylene radical, PA1 m is an integer from 1 to 40; and PA1 n is an integer of 10 or greater. PA1 A is a radical selected from the group consisting of --PO(OH).sub.2, --PO(OH)[OCH.sub.2 CH.sub.2 ].sub.y [OCH.sub.2 CH(CH.sub.3)].sub.x OR, --SO.sub.3 H, SO.sub.2 H and --H, PA1 x is a number corresponding to the degree of propoxylation; and PA1 y is a number corresponding to the degree of ethoxylation. PA1 R is a mixture of alkyl groups containing from 12 to 15 carbon atoms, PA1 Y is sulfate; and PA1 X is a monovalent cation to remove residual oil saturation from the formation pore spaces in the near wellbore area. After the treatment to improve water injectivity, the formation is waterflooded. PA1 R is a mixture of alkyl groups containing from 12 to 15 carbon atoms, PA1 m and n are nominally 7 and 2, respectively, as clarified below, PA1 Y is a sulfate group; and PA1 X is a monovalent cation.
The surfactants described therein broadly encompass those useful in the present invention, but the patent does not recognize the unique properties of the specific surfactant of this invention as to its effectiveness in lowering interfacial tension between seawater and crude oil.
U.S. Pat. No. 4,293,428 discloses injecting into a formation in a waterflooding process a surfactant having the formula: EQU RO(C.sub.3 H.sub.6 O).sub.m (C.sub.2 H.sub.4 O).sub.n YX
wherein:
Thereafter the surfactant is driven through the formation with an aqueous fluid.
U.S. Pat. No. 4,216,098 discloses waterflooding of a subterranean hydrocarbon-bearing formation with water containing a polymer comprising repeating units of vinyl sulfonic acid alkoxylated with a mixture of ethylene oxide and propylene oxide. The weight percent ethylene oxide in the mixture is about 60 to about 95.
U.S. Pat. No. 4,406,798 discloses tertiary oil recovery with oil field brine using a surfactant of the formula: ##STR1## in which: R is hydrogen or alkyl from 1 to 6 carbons,
U.S. Pat. No. 4,448,697 discloses waterflooding of a subterranean hydrocarbon-bearing formation with water containing a surfactant of the formula: EQU RO(R'O).sub.m (CH.sub.2 CH.sub.2 O).sub.n H
wherein:
U.S. Pat. No. 4,738,789 discloses a carbon dioxide waterflood which includes a surfactant having the formula: ##STR2## wherein: R is an alkyl or alkylaryl radical of about C.sub.6 to C.sub.20,